I'm still with KK, being there for them if they express doubts is fine but attempting to damage their belief system is counter productive.
The apostates that helped me out were warm and charming and we never once discussed religion unless I raised it and even then they were never critical of some of my (in retrsopect) mind blowingly crazy ideas. And I think the seed of doubt is rarely sown, we can only water it if it already exists.